1. Field of the Invention
The present invention relates generally to submersible pumps, and in particular to submersible pumps deployed in particularly hostile environments and a means and method for protection thereof.
2. State of the Art
Light duty submersible motors such as those disclosed in U.S. Pat. No. 3,631,275 and 3,814,961, employ plastic housings and may include a potting material encasing the motor within the housing. Such motors, while suitable for water pumping and vessel propulsion, do not generate a high enough output for commercial and industrial applications.
High output submersible pumps are used worldwide for many commercial and industrial pumping applications where conventional horizontal or vertical pumps are less than satisfactory. Such applications include disposition in locations which are too deep for a standard over-hung vertical pump, in those where a standard horizontal pump would require a suction lift operation or utilization of a special below-grade pump vault, and in those situations where portability is a primary or major requirement.
Submersible pumps for industrial applications which address the above situations are commercially available and generally utilize a cast iron electric motor housing and sealed stainless steel or alloy steel drive shaft. However, two hostile pumping environments which have created the most difficulty and greatest obstacle or challenge to the utilization of the submersible pumps are those which involve corrosive fluids and abrasive slurries, the latter being defined as a mixture or suspension of solids in a liquid phase. Examples of applications for submersible pumps in such hostile environments include, without limitation, the pumping of H.sub.2 SO.sub.4 -laden coal power plant groundwater runoff; processing of grapefruit, raisins, and other acidic fruits and vegetables; brine pumping; phosphate fertilizer and rock slurry handling; and the pumping and processing of a wide variety of industrial chemicals.
While corrosion-resistant materials, such as special metals, may be used to inhibit corrosion effects on exposed portions of a pumping device, these materials are generally very soft and thereby susceptible to abrasion and erosion by the swirling liquid or slurry being pumped, in which the pump itself is submerged.
It is also known in the prior art to cover certain pump parts, such as impellers and pump casings, with a rubber coating to combat the aforementioned problems. However, not only the actual pump itself but the motor driving a submersible pump is exposed to the turbulent corrosive and/or abrasive and erosive liquid surrounding the pump. Prior art attempts to protect the motor have required motor customization for hostile environment submersible applications. The two known prior art approaches have involved either the fabrication of a special stainless steel motor housing and related hardware to replace the standard cast iron housing assemblies otherwise generally employed in submersible pumps, or the coating of the motor housing with a corrosion- and abrasion/erosion-resistant epoxy coating. The former solution is, of course, expensive from both a material and fabrication standpoint, may involve housing redesign in certain instances, and possesses generally poor abrasion resistance characteristics. The latter solution is somewhat unreliable, as an epoxy coating is of low, variable thickness and bond strength, and is also easily damaged by tool usage and large particle impact actions.
As evidenced by these enumerated shortcomings of the prior art devices, there is an existing and long-felt need for a means and method of protecting a submersible pump against the effects of extremely hostile environments in an economical manner and which may be adapted to a wide variety of existing, commercially available pump designs.